An audio/visual signal can be communicated from a computing device to a display via a cable. For example, FIG. 1 is a front view of a personal computer 100 including a cable 130 connecting a computing device 110 and a display 120, such as a liquid crystal display (LCD) or plasma screen. Different standards, such as the DP standard or the HDMI standard, may be used for communicating the audio/visual signal from the computing device to the display. Under the DP standard, the transmission protocol is based on micro packets and is extensible for future feature additions, whereas the HDMI transmission protocol is a serial data stream at a 10× pixel clock rate. Also, for the DP standard, the transmission is an alternating current (AC) transmission in a voltage range of 400 mV-1200 mV. For the HDMI standard, the transmission is a direct current (DC) transmission in a voltage range of 1000 mV-1200 mV.
Each standard has advantages and disadvantages. DP supports both external (e.g., desktop) and internal (e.g., laptop) display connections whereas HDMI does not. Unlike DP, however, HDMI supports xvYCC color space, Dolby True High Definition (DolbyTrueHD), Digital Theater Systems-High Definition (DTS-HD) Master Audio bitstream, Consumer Electronics (CE) control signals, and compatibility with Digital Visual Interface (DVI). Given the different capabilities of the DP and HDMI standards, it may be useful to change data from one standard to another standard for a particular application.
FIG. 2 is a block diagram of the personal computer 100 illustrated in FIG. 1 including a conventional configuration for changing a DP transmission to an HDMI transmission using a level shifter 114. The computing device 110 includes a DP transmitter 112, whereas the display 120 includes an HDMI interface. Therefore, the DP data signal outputted by the DP transmitter 112 is changed, using a level shifter 114, into an HDMI data signal compatible with the HDMI interface on the display 120.
Specifically, referring to FIG. 2, the computing device 110 includes a system board 115. The system board 115 includes a graphics processing chip 111, a DP component 113, and a level shifter 114. The graphics processing chip 111 includes the DP transmitter 112, and the DP component 113 is coupled to the DP transmitter 112. The level shifter 114 receives the output of the DP component 113, changes the voltage level and current, and outputs an HDMI data signal. The HDMI data signal is communicated from the computing device 110 to the display 120.
In the conventional configuration illustrated in FIG. 2, the level shifter 114 is not located in the graphics processing chip 111 and is a separate chip located on the system board 115. Because the level shifter 114 is external to the graphics processing chip 111, the level shifter 114 takes up valuable hardware space in the computing device 110 and adds additional cost. Similarly, in the case of changing an HDMI data signal to a DP data signal according to a conventional configuration, an HDMI component and a level shifter external to the graphics processing chip are necessary. These external items occupy space on the system board 115, and the conventional configuration is an expensive, bulky solution for changing between HDMI transmission and DP transmission.
FIG. 3 is a circuit diagram of the conventional configuration illustrated in FIG. 2. The circuit diagram illustrates a conventional configuration for changing from DP transmission to HDMI transmission using a level shifter 114. The switching elements SN2, SN3 are controlled by a data signal D1 whereas switching elements SN1, SN4 are controlled by a complementary data signal D1 bar. Switching elements SN1 and SN2 are coupled to a current source, which is tied to ground. Switching elements SN3 and SN4 are coupled to a current source, which is biased at 2V. Switching elements SN1 and SN3 are coupled together, and switching elements SN2 and SN4 are also coupled together. Also shown in FIG. 3 is a DP component 113 including two resistors R31, R32 biased at 0.7V, and each resistor R31, R32 is coupled to a junction between the coupled switching elements (e.g., SN1 and SN3; SN2 and SN4) as illustrated in FIG. 3. Also coupled to each junction between the coupled switching elements (e.g., SN1 and SN3; SN2 and SN4) is a capacitor C31, C32. Further, in FIG. 3, a level shifter 114 is coupled to the capacitors C31, C32 as illustrated, and the output of the level shifter 114 is delivered to the receiver 121, included in the display 120 illustrated in FIG. 1. As discussed above with respect to FIG. 2, the level shifter 114 is externally used on system board for changing DP transmission to HDMI transmission. In addition, the level shifter 114 consumes valuable hardware space and the configuration is an expensive solution.